Health Officials Address Wisconsin Pertussis Outbreak

A recent outbreak of pertussis in the Milwaukee area has health officials concerned. Pertussis, sometimes called "whooping cough" because of its distinctive "whoop" or gasping cough, is a highly contagious bacterial disease that affects the respiratory tract.

In recent months, the State of Wisconsin Division of Public Health had reported an increase in pertussis activity and cases in the southeast region of the state. As a result, local public health agencies and healthcare providers were asked to enhance surveillance and reporting of pertussis.

The Milwaukee Health Department (MHD) has been actively monitoring for pertussis in the city over the past six months. By early June, nearly 50 cases of the disease had been confirmed in Milwaukee County, and the numbers continue to rise.

Pertussis activity, which typically runs in regional epidemics, "Is probably more common than previously recognized," says Michael Chusid, MD, Professor and Vice Chair of the Department of Pediatrics at the Medical College. "Our recent 'outbreaks' may be more due to greater clinical awareness of the milder form of the disease in older patients and better diagnostic tests, than to a real increase in infection prevalence."

Symptoms Differ in Infants, Adults
Pertussis spreads quickly and easily through the air when an infected person coughs or sneezes. Exposure usually occurs after close indoor face-to face contact, such as people sharing the same household. In fact, the CDC reports that pertussis has a secondary attack rate of 80% among susceptible household contacts.

In infants, pertussis can be quite dangerous, says Dr. Chusid. "Symptoms similar to those of the common cold, such as runny nose, watery eyes, and low-grade fever, are followed by episodes of severe spasmodic coughing," he notes.

Following the cough, children may make a loud whooping sound as they struggle to inhale air. Severe coughing attacks can cause infants to stop breathing temporarily (apnea) and turn blue because of low oxygen levels (cyanosis). If severe spells continue long enough, some infants can have seizures or even die. Even with treatment, coughing may last for months.

Adults can develop a milder form of the disease (regardless of previous vaccination), but unvaccinated infants and children under the age of one with pertussis are the most susceptible and much more likely to become very seriously ill.

"In older children and adults, pertussis usually shows up as a chronic cough, which is frequently worse at night. There is usually no fever," Dr. Chusid says. The cough may last for weeks to months and may be spasmodic.

Because symptoms of pertussis might be seen as annoying rather than disabling in adults, infected individuals are likely to continue to go to school or work and not seek medical attention. This appears to have been the case in the Milwaukee-area outbreak, where several of the infected adults were students at the University of Wisconsin-Milwaukee.

The MHD, along with the Shorewood Health Department, State of Wisconsin Division of Public Health and the Norris Student Health Center at the University of Wisconsin-Milwaukee, are conducting a follow-up investigation of students with confirmed or probable pertussis infection.

The investigation includes identifying persons who came into close contact with the students during the period in which they were symptomatic and could transmit the disease. The MHD has distributed approximately 2,000 letters to UWM students in an effort to identify others who might possibly have been exposed to the disease.

Treatment
"Pertussis is treated with multiple types of antibiotics, usually Azithromycin for 5 days or Erythromycin for 2 weeks. Penicillins are not effective," Dr. Chusid reports. Treatment does not change the course of illness unless given extremely early in the course of infection. However, it usually eradicates the Bordetella pertussis bacterium in about 5 days so that the patient can no longer transmit the infection to others.

Symptoms generally don't improve much during treatment because by the time the diagnosis is made, the lining of the respiratory tract has sustained some damage, and it takes time to heal. In severe cases the epithelial lining might never fully regenerate.

Vaccination is Critical
Vaccination, especially of infants, is critical for preventing this serious illness. "The risks of the disease far outweigh any risks of the vaccine," Dr. Chusid notes. "In countries where they've cut back pertussis vaccination, there has been a huge increase in infant mortality due to pertussis."

The DtaP vaccine (diphtheria and tetanus toxoids and acellular pertussis) is available for children aged two months to six years, and all parents of children in this age group should make sure that their children's DTaP vaccines are up to date.

The DTaP vaccine has a low risk of side effects and is recommended for all infants at 2, 4 and 6 months of age. Additional booster doses of DTaP are recommended at 15-18 months of age and at 4-6 years of age. It is important that young infants start their DTaP vaccination without delay at 2 months of age.

The original whole-cell pertussis vaccine DTP vaccine (diphtheria, tetanus and pertussis) posed a higher risk of side effects in older children and adults, and could not be given to anyone over 7years of age. Concerns about safety led to the development the more purified (acellular) pertussis vaccines used today.

Before the introduction of routine pertussis vaccination in the 1940s, pertussis was a major cause of serious illness and death among infants and young children in the United States, with more than 200,000 cases reported annually.

Since widespread use of the vaccine began, incidence has decreased more than 98%, but that still means 5,000 to 7,000 cases of pertussis are reported each year in the United States. In 2003, 13 infected children died. Most were unvaccinated or too young to be vaccinated.

"Complete immunity from the vaccine that today's adults received when they were children probably lasted only about 10 years," says Dr. Chusid. "Partial immunity remains for decades, so immunized individuals don't get the severe infection, but they do get the chronic cough, and can be a risk to others.

"Studies are underway in adults to see its safety and effectiveness in maintaining immunity," Dr. Chusid reports. "It's possible in the near future the DTaP vaccine will be recommended for adults to receive periodically."

Dr. Chusid recommends that adults with an unexplained chronic cough that lasts more than 7 to 10 days should see their physician and be tested for pertussis, especially if the coughing is explosive and occurs in spasms.

All individuals with a cough should practice appropriate preventive measures including good respiratory hygiene (covering nose and mouth when coughing or sneezing) and good hand washing. People with chronic, unexplained coughs should not have close contact with infants until evaluated for pertussis or other infectious diseases.

P.J. Early
HealthLink Contributing Writer

This article includes information from the US Centers for Disease Control and Prevention and the Milwaukee Health Department.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.